It is well known that overall fuel efficiency in a multiple-cylinder internal combustion engine can be increased by selective deactivation of one or more of the engine valves, under certain engine load conditions. For example, for an overhead-cam engine, a known approach to providing selective deactivation is to equip a valvetrain member such as the hydraulic lash adjusters for the overhead-cam engine valvetrains with means whereby the roller finger followers (RFFs) may be rendered incapable of transferring the cyclic motion of engine cams into reciprocal motion of the associated valves. Typically, a DHLA includes, in addition to the conventional hydraulic lash adjuster, a concentric inner pin housing and outer HLA body which are mechanically responsive to the force of the RFF as exerted by the cam lobe, and which may be selectively latched and unlatched hydromechanically to each other, typically by the selective engagement of pressurized engine oil on locking pins.
An important consideration in a DHLA is the amount of internal mechanical lash deliberately incorporated into the DHLA. In prior art DHLAs, a transverse bore in the pin housing contains the two opposed locking pins which are urged outwards of the pin housing by a pin-locking spring disposed in compression therebetween to engage a first annular groove including a locking surface (also referred to herein as “pin shelf”) in the inner wall of the HLA body whereby the HLA body and the pin housing are locked together to produce reciprocal motion of an RFF disposed on the DHLA. When valve deactivation is desired, the pins are withdrawn from the DHLA body by application of hydraulic fluid such as engine oil to the outer ends of the pins at pressure sufficient to overcome the force of the pin-locking spring.
Prior art DHLAs also are assembled from a top end of the DHLA body (which is closed at its bottom end) by insertion of components through the open top end and securing the components with one or more retaining rings into a second annular groove formed in the inner wall of the DHLA body near the open end thereof. The rings used to secure the components also serve to set internal mechanical lash in the DHLA by the selection of rings of appropriate thickness during assembly of the DHLA. Thus, the rings act as a mechanical stop to limit the outward motion of the pin housing prior to engagement and disengagement of the locking pins. With the lost motion springs applying an upward force on the pin housing to force the top surface of the ring against the top of the annular groove, the lash rings permit the pin housing to travel to a position wherein the locking pins can clear the bottom surface, or pin shelf, of the locking groove in the DHLA body by a small amount, typically about 0.005 inches or less. Excess clearance or internal mechanical lash results in clatter and wear of the DHLA during engine operation. Variations in internal mechanical lash can also adversely affect the opening and/or closing timing of the associated valve. Thus, the axial position of the underside of the retaining rings with respect to the locking groove pin shelf is of critical importance.
Typically, because of variation in manufacturing tolerances of the body, pin housing, and pins, the correct lash is obtained only by iterative trial and measurement using lash-adjusting rings of differing thicknesses. Setting the lash in this fashion is difficult and complicated. Moreover, since setting lash in this fashion relies on the machined integrity of the top surface of the annular groove, machining difficulties inherent in forming the top surface of the groove can result in unnecessary variances in mechanical lash settings.
What is needed in the art is an improved DHLA wherein components are easily assembled and wherein mechanical lash is easily set in a single, simple procedure.
It is a principal object of the present invention to reduce the cost and complexity of an improved DHLA, and to improve the ease and reliability of assembly thereof.